1. Field of the Invention
This invention relates generally to fluid pressure regulating systems, and more particularly to systems for stabilizing the delivery flow of water and chemicals to a wafer preparation station.
2. Description of the Related Art
As is well known, semiconductor devices are fabricated from semiconductor wafers, which are subjected to numerous processing operations. These operations include, for example, impurity implants, gate oxide generation, inter-metal oxide depositions, metallization depositions, photolithography pattering, etching operations, chemical mechanical polishing (CMP), etc. Although these processes are performed in ultra clean environments, the very nature of many of the process operations is to blame for the generation of surface particles and residues. For instance, when CMP operations are performed, a film of particles and/or metal contaminants are commonly left behind.
Because surface particles can detrimentally impact the performance of an integrated circuit device, wafer cleaning operations have become a standard procedural requirement after certain process steps. Although cleaning operations are rather procedural, the equipment and chemicals implemented to perform the actual cleaning are highly specialized. This specialization is important because each wafer, being at different stages of fabrication, represents a significant investment in terms of raw materials, equipment fabrication time, and associated research and development.
To perform the cleaning operations in an automated manner, fabrication labs typically employ a cleaning system. A typical cleaning system may be, for example, a Synergy.TM. cleaning system from OnTrak.TM. of Lam Research Corporation, Fremont, Calif. A typical Synergy.TM. cleaning system employs two brush stations, where each brush station has a set of brushes for cleaning the top and bottom surfaces of a wafer. Each of the brushes are commonly configured to deliver chemicals and DI water Through-The-Brush (TTB) or by way of a drip dispensing bar, to enhance the cleaning ability of the system. The system typically also includes a spin-rinse station, where a wafer, after being cleaned in the brush stations is rinsed with DI water and dried before completing the cleaning cycle.
As can be appreciated, it is very important that facility lines, which supply the DI water to the cleaning system supply the water at substantially steady water pressure levels. Unfortunately, the facility lines in different fabrication labs vary substantially. Thus, the delivered water can have fluctuating pressures that cause more or less water to be supplied during a wafer preparation operation. On the same token, it is very important for facility lines, which supply chemicals to a system deliver a steady flow to internal modules that mix DI water with the delivered chemicals.
For instance, in cases where the chemical solution is hydrofluoric (HF) acid, if too much HF acid may be mixed with DI water, the resulting solution can be too strong and therefore cause over etching to occur. In other cases, not enough DI water is mixed with HF acid, which can also produce an over concentrated solution. The possibility of over etching, under etching, or just simply inappropriate wafer surface preparation can cause dies of a prepared wafer to be unreliable or damaged.
In view of the foregoing, there is a need for systems and methods for stabilizing DI water and chemical delivery to wafer preparing systems.